Aspects of the present invention relate generally to Power over Ethernet technologies, and more particularly to a system and method of determining an unbalanced current condition in Power over Ethernet applications.
Recent technological and market developments have resulted in a growing interest in Power over Ethernet (PoE) applications such that many network equipment manufacturers and systems integrators are endeavoring to design and implement enhancements to PoE. PoE has been standardized in a specification promulgated by the Institute of Electrical and Electronics Engineers (IEEE), specifically, the IEEE 802.3af standard for providing power to data terminal equipment (DTE) via a medium dependent interface (MDI).
In operation, PoE is similar to that of a traditional telephone network in which operating power necessary for the electrical components in the telephone is delivered from the central office through the telephone cable, i.e., it is not necessary to couple the telephone to an independent external power source. In PoE implementations, power is typically delivered to DTE devices from Ethernet switches or power sourcing equipment (PSE) via the local area network (LAN) cabling itself. Operating power provided through the LAN cables is then employed to power Internet Protocol (IP) telephones, wireless access points, security or web cameras, and the like. This technology does not require alteration of the Ethernet infrastructure, and eliminates the requirement that networked DTE devices be supplied with operating current from an independent external power source.
It is expected that the existing IEEE 802.3af standard will soon be augmented by another specification, IEEE 802.3at (or PoE+), which is under development. As currently contemplated, PoE+ will support increased current requirements, and accordingly, some of the challenges associated with supplying direct current (DC) power over category 5 (Cat5) or category 3 (Cat3) network cables will be exacerbated by the higher current levels prescribed by IEEE 802.3at. One potential impediment is a current mismatch between the positive and negative (+/−) wires of a given twisted pair. In some instances where the current is not equal, a net induced magnetic field can saturate transformers and decrease effective open circuit inductance (OCL), thus causing droop and other signaling degradation. Various factors may influence such a current mismatch including, but not limited to, different respective resistances in the +/− wires, and different contact qualities or contact resistances at the connections. Regardless of the source of the mismatch, however, the end result is the same; attendant signal degradation can cause packet errors or even link instability or failure.
Hence, it may be desirable in some circumstances to provide a method and system that effectively identify an unbalanced current condition in PoE applications.